1. Field of the Invention
The present invention relates to a light emitting device, such as a semiconductor laser, a light-emitting diode or the like, having an active layer and a layer subjected to impurity injection.
2. Description of the Related Art
In a current-injection type light emitting device such as a semiconductor laser, a light emitting diode or the like, in order to improve a current introduction efficiency and a light emission efficiency, a pn junction position and a position of an active layer are preferably set closer to each other. For the same reason, it is preferable to increase concentration of the introduced impurity to a higher level.
However, when impurities of a certain kind are injected into the active layer, the active layer is considerably rapidly deteriorated. Therefore, there are usually employed some countermeasures therefor such as a process of lowering a concentration of the injected impurity in the vicinity of the active layer, a process of separating impurities from the active layer by setting the vicinity of the active layer as a non-doped layer, or the like.
As described above, a doping profile in the vicinity of the active layer is a very important factor which influences reliability of the light emitting device.
Especially, when a III-V compound semiconductor such as GaAs, GaInP or the like is doped with zinc, zinc is very easily diffused and hence easily enters the vicinity of the active layer during crystal growth at a high temperature, which leads to deterioration of the light emitting device (see Endo et al.: Appl. Phys. Lett. 64(1994), p146).
Specifically, if an impurity diffusion region is too close to the active layer, then a lifetime of the light emitting device is lowered, and thereby its reliability is lowered. If, on the other hand, the impurity diffusion region is too far from the active layer, then the position of the impurity diffusion region is displaced relative to the pn junction.
Therefore, although the condition of the introduction of the impurity is an important factor in the light emitting device, it is difficult to control the diffusion of the introduced impurity such as zinc or the like, which considerably lowers a degree of freedom in the doping profile.